1. Field of the Invention
The present invention relates to an oil-free type vane pump which is utilizable as a supercharger for an internal combustion engine, and more particularly to a vane pump of the type having a device for regulating a vane movable in a rotor which is rotatably disposed at an eccentric position within a center housing.
2. Description of the Prior Art
The known oil-free type vane pump has a vane of which the tip slides along the inner surface of the center housing upon rotation of the rotor. The tip is forced to the inner surface of the center housing by a centrifugal force due to the rotation of the vane. This results to a disadvantage that a frictional loss rapidly increases between the tip of the vane and the inner surface of the center housing when the pump runs at high speeds.
In JP A 54-5207, a vane pump is shown with a plurality of vanes radially movable in a rotor and guide means for regulating the vane and receiving a centrifugal force exerted by the vane. The means comprises front and rear annular cam grooves formed in front and rear housings and front and rear guide pins, as cam followers, secured to both sides of each vane, whereby the annular cam grooves guide the motion of the vane and receive the centrifugal force through the intermediary of the pins. The annular cam groove has a cross-sectional profile similar to the inner surface of the center housing.
However, the vane pump as described above has disadvantages one of which is that the annular cam groove soon wears and can not be used for a long time. The reason for this is that the radial vane always has a large radius of gyration to bring a large centrifugal force when the rotor runs at high speeds and that the large centrifugal force presses the pin on the inner surface of the guide hole. Another disadvantage is that the vane pump has an efficiency lower than usual because of having a relatively large clearance between the tip of the vane and the inner surface of the center housing. When the inner surface of the center housing is circular in cross-section, the pin must follow in a non-circular path to guide the tip of the vane along the inner surface of the center housing or keep a constant clearance therebetween. Therefore, the clearance can not be kept constant where the annular cam groove and the inner surface of the center housing are cross-sectionally similar in profile to each other.